This invention relates to a process for converting crude copper phthalocyanine into xcex2-phase copper phthalocyanine pigment.
Crude copper phthalocyanine (CuPc) pigment is non- or partially-substituted and when obtained directly from solvent or non-solvent synthetic routes is generally in a coarse crude form that is non-pigmentary, tinctorially weak, and requires further processing. By xe2x80x9ccrudexe2x80x9d we mean a pigment obtained in a highly aggregated form having a particle size not suitable for use as a pigment, or pigment which has been milled to produce a product which is also aggregated and has a broader particle size distribution than that obtained from synthesis but is still unsuitable for use as a pigment or an industrial colorant for inks and/or coatings. This processing involves comminution (e.g. milling) to reduce the particle size, and/or further conditioning to obtain pigmentary quality. Several conventional primary comminution processes include, for example, dissolving or swelling crude pigment in different concentrations of sulfuric acid, precipitating it in water, and kneading it in combination with milling aids (i.e., inorganic salts) and solvents. Wet milling or dry milling are typically carried out for example in a ball mill with or without milling aids. When the primary route of comminution is by dry grinding, typical a conditioning process follows and may include: slurrying or suspending the milled-crude in an aqueous, aqueous-organic or organic solvent and heating and/or wet-milling, or mixing in a dense mass state with water-soluble solvent and inorganic salt to provide pigmentary quality material.
Pigment processing by wet and dry milling of crude organic pigments is described in the prior art. They often require conditioning the wet or dry milled crude pigment in a slurry, at an elevated temperature, with large amounts of water, solvent, surfactants and/or combinations of these along with other additives. The fluids used are typically used in the range of up to 100 wt. % or more of the milled crude.
It is desirable, however, to minimize the amount of water, organic salts, solvent and additives used during pigment synthesis process since most of these compounds or solvents must be removed in order to isolate the CuPc pigment. This can be time-consuming and thus expensive. Furthermore, using less organic solvents is preferred because of environmental considerations. Lower process temperatures are also preferred as this helps to minimize crystallite growth and this is important since larger pigment crystals lose color strength and are more opaque.
The present invention relates to a dry process for producing xcex2-phase CuPc pigment and with excellent color value. Specifically, the xcex2-phase CuPc pigment is prepared by grinding crude CuPc in the absence of grinding aids then dry conditioning in a conditioning solvent that is present in low amounts.
It has now been found that pigmentary grade phase CuPc can be produced by dry grinding crude CuPc in the absence of grinding aids to obtain a crude mill and subsequently conditioning the crude mill in the presence of a low amount of conditioning solvent.
The first process step of the present invention involves dry milling, in an industrial grinding mill such as a ball mill, attritor, or vibratory mill, the crude. No grinding aids (i.e. inorganic salts) are present during milling. The milling conditions, which include the grinding media size, shape and composition, milling time and temperature, are mill dependent. The aggregated product (e.g. crude mill) will be an xcex1:xcex2 mix mostly of the xcex2-phase and have, as determined by X-Ray diffraction, i.e. from 0:100 to 80:20. More preferably the target xcex1:xcex2 ratio is from 50:50 to 65:35 when no milling solvents are present and from 0:100 to 65:35 when milling solvents are used. The crude mill will have a surface area, of less than 10 m2/gm and consists of primary particles of less than 0.10 microns in size. The dry milling step may also be performed in the presence of low amounts of milling solvent and other additives.
Milling solvents may be used in amounts less than 50% preferably 10% of the weight of the crude CuPc, and at combinations of these along with other additives. The fluids typically are employed in amounts ranging up to 100% by weight or more of the crude mill.
The second process step of the present invention involves conditioning the crude mill, for example, in an industrial mixer to a free-flowing granular powder form with a conditioning solvent and optionally a dispersant or other additive to form. The dry magma which is formed shall contain about 25 to 95 wt. %, preferably about 45 to 65 wt. % of the crude mill; conditioning solvent weighing about 5 to 50 wt. %, preferably about 20 to 40 wt. % of the crude mill; dispersant being about 0 to 20 wt. %, preferably about 5 to 15 wt. % of the crude mill; and additives (such as resins or waxes) being about 0 to 50 wt. % of the crude mill. The crude mill is then conditioned and/or recrystallized by mixing under shearing for 1 to 15 hours, preferably for 2 to 8 hours, at a temperature of less than about 120xc2x0 C., more preferably between about 80 to 110xc2x0 C., and most preferably between about 90 to 100xc2x0 C. in an industrial mixer.
Industrial mixers include but are not limited to a sigma or disperser blade mixer, a double planetary mixer, a vacuum drier with or without rotating chopper blades, a conventional dough mixer, a mix muller, an extruder or any mixing or grinding unit that is capable of applying a mechanical shear or mixing.
Milling and conditioning solvents are used here to describe organic materials that are non-solid at the conditioning temperature and pressure. The conditioning solvent may be of a recrystallizing type or a non-crystallizing type, with the recrystallizing type preferred when the crude mill contains xcex1-form CuPc that needs to be recrystallized to xcex2-form CuPc. When all form CuPc crude mill is obtained either type of solvents may be used. Incorporated into the scope of this invention is that any combination of the two types, or two or more of either types may be used, though a single solvent is preferred.
Preferably, the conditioning solvent is selected from the group consisting of glycols, fatty acids, plasticizers (such as dioctyl phthalate and nonylphenolethoxylates), hydrocarbon petroleum distillates, and alkylene carbonates. More preferably, the conditioning solvent is a glycol such as a glycol selected from the group consisting of diethylene glycol, dipropylene glycol, polyethylene glycol, monoethylene glycol monoether, triethylene glycol monoether, and glycol ether esters (such as butyl carbitol acetate).
Pigment dispersing agents and other conventional additives may be added before, during or after the dry grinding, conditioning or isolation processing steps. They help improve wetting, dispersibility, dispersion stability and coloristic properties (strength, gloss, transparency, etc.) of the CuPc pigment.
Examples of dispersants include but are not limited to CuPc-(X)n, wherein n is an integer from 1 to 6; X is selected from the group consisting of SO3xe2x88x92M+, SO2R, and CH2Y; M is selected from the group consisting of hydrogen, primary, secondary, tertiary, or quaternary amine; R is selected from the group consisting of metal ion, dimethyl amino propylamine, phthalimide, and amine terminated polyalkylene oxide; and Y is selected from the group consisting of NH2, phthalimide, and o-carboxy benzamide.
Examples of conditioning additives include but are not limited to various types of rosins, polymeric resins, waxes, plasticizers, crystal growth inhibitors and extenders.
The resulting CuPC pigment product can be further processed or incorporated directly into, for example, an ink formulation to provide excellent color value.
An optional third process step can be employed in the present invention when it is desirable to isolate the pigmentary CuPC product. It involves isolation of the pigment by removing the milling or conditioning solvents and can be performed by distillation, filtration or by other methods known to those ordinary skill in the field of solvent removal. The presscake obtained from using a conventional filter press typically employed at the end of a solvent removal step may be dried and ground by conventional methods known in the field. However, solvent removal may be avoided altogether if the milling and conditioning solvent, dispersant and additives have specifically chosen to remain in the product as having compatibility with the final application of the product as a colorant.